It has long been known to perform pipe bending with highly flexible, CNC-controlled bending machines, with measures being used which support the material properties in the limit areas in order to achieve reproducible bending results without any material failure. Such supporting measures include the use of internal mandrels, slide rails or fold smoothers, with the use of internal mandrels in a pipe bending machine being used especially for internal support of the pipe during the bending in the bending area. This should prevent that undesirable deformations, fissures, folds or the like occur in the pipe during bending.
The internal mandrel device usually consists of a mandrel element which is fastened to a mandrel bar which on its part connects the mandrel element with a traveler which is connected to a feed device in order to axially displace the mandrel element in the pipe. This known method usually only works with pipes which have been cut to respective lengths and are supplied to the bending machine successively. After the insertion of the workpiece, the internal mandrel is inserted into the pipe from behind and positioned in the bending region. The feed device is attached axially behind the pipe.
It is often desirable in the area of small diameters to process endless pipe material from the coil. In this case however it is no longer possible to insert an internal mandrel from the end of the pipe, so that in this case it is necessary to bend without the internal mandrel. This leads to the consequence however that desired bends with narrow bending radii can often not be produced.
It is also often the case that very long workpieces that are cut to size are available which cannot be processed with internal mandrels on conventional machines, but which require special longer machine assemblies or need to be shortened to a respective length, leading to a high amount of waste however.
Such machines are also known which work directly out of the sheet material, form the same at first into a pipe and then bend it. The internal mandrel is inserted into the pipe region that has not yet been closed.
The use of ice as the material for an internal mandrel is further known.
The use of floating mandrels during pipe drawing is also known in the state of the art.
EP 1 484 123 B1 describes a machine in which a pipe is formed from a sheet which is subsequently formed by bending. The mandrel unit is arranged to be offset to the rear to such an extent that it engages from above into the still open profile and thus positions the mandrel element in the bending area. This known method does not work in the case of profiles that have already been closed such as finished pipes.
An apparatus is known from DE 28 16 840 in which a pipe is formed from a sheet which is formed again subsequently by bending. It is proposed here to use a frozen or solidifiable material (ice) for the internal mandrel. The use of fluids or other solidifiable materials is actually undesirable, is not suitable for all pipe materials and is also unable to withstand the high pressures during bending.
U.S. Pat. No. 3,891,952 describes an apparatus for producing fins on pipes by rollers. An internal mandrel is inserted into the pipe as a counterholder against the roller pressure, which mandrel is axially fixed in a respective position via an external magnet. The internal mandrel is not used in conjunction with bending machines.
The same also applies to the pipe drawing apparatus of DE 37 39 730 C1 where a magnetically held mandrel is used during pipe drawing. It does not concern an internal mandrel for bending machines however.
There is a need to provide an arrangement for bending tubular workpieces of the kind mentioned above, with which pipes of any desired length, which also include endless pipes from the coil or pipes tapering on one side or formed in another way and which prevent the insertion of the internal mandrel from behind, can be bent with an internal mandrel without limiting the use of the internal mandrel device by the length of the workpiece or the length of the machine.